An electric machine such as an electrical motor, power generation system, genset, or the like, is generally used to convert one form of energy into another and may operate in a motoring mode to convert electrical power into rotational or otherwise mechanical power, or operate in a generating mode to convert rotational or otherwise mechanical power into electrical power. Among the various types of machines available for use with an electric drive, switched reluctance (SR) machines have received great interest for being robust and cost-effective. While currently existing systems and methods for controlling such electric machines provide adequate control, there is still room for improvement.
Among other factors, proper detection or estimation of the initial position of the rotor relative to the stator of the SR machine, while at rest or at an otherwise substantially low machine speed, is essential to the performance and efficiency of the SR machine. Some conventional control schemes rely on a mechanically aligned speed wheel and corresponding sensors to detect and determine the initial position of the rotor relative to the stator at machine startup. However, such control schemes have been frequently found to be susceptible to error, thus resulting in substantial losses in efficiency during operation. For instance, an error of 2 degrees in the detected mechanical rotor position of an SR machine, caused by a skewed sensor, a mechanical misalignment of the speed wheel, or the like, may correspond to a 0.5% decrease in efficiency of the electric drive assembly at full load.
Sensorless control schemes also exist and derive or calculate the initial rotor position using electrical characteristics of the SR machine. However, as with the sensor-based schemes, these electric drive assemblies have also been found to be deficient and susceptible to much error. Specifically, the theoretical models upon which the derivations are based, when reduced to actual experimentation or practice, were often found to cause substantial deviations from the desired effects in terms of machine performance and efficiency. Furthermore, the accuracy of currently existing sensorless control schemes have been found to be easily affected by normally occurring changes in the associated electric drive, such as the common bus or direct current (DC) link voltage.
Accordingly, there is a need to provide a control system or scheme for estimating the initial position of a rotor of an SR machine that enables more efficient operation and performance of the SR machine. Moreover, there is a need to provide an initial rotor position estimation means that is more reliable, more accurate, less susceptible to a varying DC link voltage and easier to implement. There is also a need to minimize torque production so as to substantially minimize any undesired movement of the machine. The systems and methods disclosed are directed at addressing one or more of these needs.